Non-indigenous species continue to be dispersed to new environments. The New Zealand mud snail (Potamopyrgus antipodarum) was identified in the Great Lakes in 1991 and, more recently, identified on the west coast of Canada in 2006. This snail possesses many traits making it well suited for invasions including a high reproductive rate and a broad range of environmental tolerances. Its life-history characteristics enhance long-distance natural dispersal while further dispersal via a number of human-mediated vectors is probable. In some systems, this small snail reaches extremely high densities and can alter ecosystem services and trophic relationships by grazing primary producers, outcompeting native invertebrates, and negatively influencing higher trophic levels. Based on impacts of New Zealand mud snail elsewhere, and owing to their extensive invasion history in Europe and the western United States, there is considerable concern about the potential ecological impacts if New Zealand mud snail spreads in Canada, especially to inland freshwater or other coastal ecosystems. Fisheries and Oceans Canada conducted a national risk assessment, including a peer-review workshop during March 2010, to determine the potential risk posed by this non-indigenous gastropod to Canadian coastal and inland waters. This assessment evaluated the probability of arrival, survival, reproduction, and spread and associated potential consequences (impacts) to determine risk. These components were assessed using an expert survey and an expert workshop using the best available information on the biology, potential vectors of introduction, and impacts in both native and introduced ranges. This assessment also incorporated measures of environmental suitability from an ecological niche model and bedrock geology to identify locations with calcium deposits required for shell building. The risk assessment, based on a widespread invasion, concluded that the New Zealand mud snail generally posed low risks to most Canadian aquatic ecosystems with a moderate risk posed to freshwater biodiversity in most Canadian freshwater drainages. However, at smaller spatial scales the risk posed by this species could be much higher. Further, considerable uncertainty identified for some stages of the invasion cycle highlights the need for additional research, especially about potential impacts of this gastropod in Canadian ecosystems, as this information is critical for potential management.
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